Numbering

Area Code Information - Detailed information on the history and current developments in North American NPA allocations.
www.areacode-info.com/

International Numbering Plans - A collection of all international numbering plans in the world. Some features require a paid subscription.
www.numberingplans.com/

800 Service Management System - Information about the central database for US toll free number management.
www.sms800.com/

The Telephone Exchange Name Project - The historical relationship between North American telephone exchange names and numbers.
ourwebhome.com/TENP/TENproject.html